Management and prevention of soft tissue complications in implant dentistry

Abstract The management and prevention of soft tissue complications is of key importance in modern implant dentistry and influences biologic and esthetic outcomes. The assessment of the soft tissue conditions from a quantitative and qualitative perspective should, therefore, be part of the overall treatment plan. Such an assessment dictates a potential indication as well as an ideal time point for additional soft tissue management. A proper risk assessment and management of the soft tissues at the planned implant site are of key importance prior to any implant‐related surgery. Cases with peri‐implant soft tissue complications generally involve: (a) a lack of attached and keratinized mucosa; (b) insufficient volume; (c) development of mucosal dehiscences; or (d) a combination of (a), (b), and (c). In case of soft tissue deficiencies, these should be addressed as early as possible to increase the predictability of the surgical interventions. This article reviews the main causes for peri‐implant soft tissue complications and presents different therapeutic options for the management of various clinical scenarios.


| INTRODUC TI ON
Dental implants are frequently used to support fixed and removable prostheses in partially and fully edentulous patients. Based on recent systematic reviews including a plethora of clinical studies, high survival rates can be expected at both the implant and the restorative level. 1,2 For a long time, implant research was focused on the periimplant bone, establishing hard tissue quality and quantity as being the principal criteria for defining success. 3 Therefore, adequate bone volume was a prerequisite prior to implant placement, with various ridge preservation and augmentation procedures performed accordingly. 4 A facial bone thickness of at least 2 mm was suggested to maintain marginal bone levels around the implant over time. 5 Crestal bone loss 6 and primary implant stability 7 were considered as the critical factors for success, whereas the importance of the peri-implant soft tissues was frequently neglected.
More recently, emerging evidence suggests that the peri-implant soft tissues are key to maintaining peri-implant health. 8 Current longterm clinical studies have shown stable and healthy peri-implant soft tissues after 7 9 and 12 years 10 , even in the case of missing buccal bone at implant sites.
The present narrative review focuses on the management, timing, specific interventions, and the prevention of soft tissue complications in implant dentistry. Besides the evidential background, this article provides a time line and a risk scale for different interventions to prevent and manage soft tissue complications.

| ANATOMY OF THE PERI -IMPL ANT MUCOSA AND SUSCEP TIB ILIT Y TO INFL AMMATION
The anatomy of the peri-implant mucosa differs from the gingiva around natural teeth. First, the peri-implant connective tissue fibers run parallel to the implant surface and, in general, do not attach to it, whereas the dento-gingival fibers show a perpendicular disposition, attaching directly to the root cementum. 21 Second, the vascular supply at implant sites is diminished because there is no periodontal ligament present and the only source of nourishment is derived from the supra-periosteal blood vessels. 22 Third, the junctional epithelium around implants is more permeable and its connective tissue compartment shows fewer fibroblasts and a greater number of collagen fibers. 23 These anatomical differences render dental implants more susceptible to inflammation and subsequent bone loss from microbial challenge. 24 The maintenance of an adequate quantity and quality of mucosa surrounding the peri-implant bone has been demonstrated to be of paramount importance in maintaining periimplant health. 25 Peri-implant health is characterized by the absence of bleeding on probing and stable marginal bone levels. Peri-implant mucositis is defined as the presence of bleeding on probing and/or suppuration but without any evidence of bone loss. Peri-implantitis requires progressive crestal bone level changes, in addition to bleeding on probing and/ or suppuration, with or without deepening of peri-implant pockets. 26 Indeed, there is increasing evidence demonstrating that the long-term maintenance of peri-implant health is a difficult challenge and that trans-mucosal healing and adequate management of the peri-implant mucosa may be a decisive factor in avoiding the development of complications. In addition, a recent systematic review recommended soft tissue augmentation procedures to maintain and improve peri-implant health at dental implants, suggesting that these procedures limit marginal bone loss and reduce the incidence of bleeding on probing over the long term. 28

| SOF T TISSUE COMPLIC ATIONS AROUND IMPL ANTS
Three types of soft tissue complications may develop around dental implants and represent an everyday clinical challenge, namely, a lack of attached mucosa, volume deficiency, and peri-implant mucosal recession.
After tooth extraction, a significant reduction in the ridge dimensions occurs. [29][30][31] This shrinkage of the alveolar ridge is not limited to the bone but may also be accompanied by a loss of attached tissue and/or a soft tissue volume deficiency. 32 The incidence of a complete absence of an adequate band of attached and keratinized tissue has been reported to range from 46% to 74% of all inserted implants. 33 By contrast, incidence data for the lack of mucosal volume around implants has not been reported in the literature because of the difficulties in assessing it in a noninvasive manner. Data, however, suggests that it is a common finding among implants placed in the esthetic zone and its occurrence plays a role in the mucosal color match of implants compared with their adjacent dentition. The color of the peri-implant tissues matches those of the neighboring teeth in only 33% of cases. 34 This mismatch is more obvious in thinner biotypes, where a discoloration may still be clinically noticeable. 35 This, to some extent, underlines the necessity to perform soft tissue grafting procedures, predominantly in the esthetic zone.
The occurrence of recession defects on the buccal side of dental implants is influenced by various factors, such as tissue phenotype, facial bone level, implant angulation and axis, interproximal marginal bone level, implant design, and the level of first bone to implant contact. 36 The incidence of such recession defects varies, depending on the time point when dental implants were placed. For immediate implants, an advanced recession at 10% of implants has been reported, 37 whereas for delayed implants, > 1 mm of midfacial soft tissue recession can be expected in 60% of implants. 38 All three types of soft tissue complication are, therefore, a common clinical finding and may hamper peri-implant health and the esthetic outcome of implant-borne reconstructions.

| Attached mucosa
The influence of a sufficient width of attached tissue around dental implants still remains controversial in the dental literature. A consensus report from the Consensus Conference of the European Association for Osseointegration 39 stated that "there is a lack of high-quality studies evaluating the need for attached mucosa around implants to maintain health and tissue stability." By contrast, recent systematic reviews demonstrated that a deficient band of attached tissue around implants is associated with greater plaque accumulation, mucosal inflammation (assessed by bleeding on probing), development of soft tissue recession, and patient discomfort while performing oral hygiene. 11,13,40

| Soft tissue volume
Soft tissue volume refers to the vertical and horizontal thickness of the peri-implant tissues and is important for the formation of a biologic width around implants. Peri-implant bone undergoes a remodeling process to allow sufficient space for the peri-implant soft tissue to be formed. 41,42 The assessment of soft tissue volume is challenging because of the scarcity of measuring tools able to evaluate soft tissue changes. The introduction of digital optical scanning/analysis as an assessment method has allowed measurement of changes in soft tissue volume over time. 43 Indications for mucosal volume augmentation include esthetic improvements, prevention of recession, facilitation of oral hygiene, and maintenance of marginal bone and peri-implant health.
Horizontal tissue thickness (measured on the buccal side of the implant) has been associated with buccal tissue stability, 8,44 less marginal bone loss, 45 and improved esthetic outcomes. 35 Moreover, a sufficient vertical thickness of the mucosal tissues (measured coronal to the implant) has been associated with decreased marginal bone loss compared with thinner biotypes. 46,47 As shown in a recent systematic review, 28 soft tissue grafting procedures for gain of mucosal thickness resulted in significantly less marginal bone loss over time.

Management of lack of attached mucosa:
(A) before implant placement: highly recommended.
(B) with implant placement: less recommended.
(C) within the implant-healing phase: less recommended.
(E) after delivery of the implant reconstruction: less recommended.

| Buccal soft tissue recession
Peri-implant soft tissue recession can be a major esthetic complication, predominantly when occurring in the anterior maxilla. A number of factors appear to influence the level of the marginal mucosa. 36 Those that have been shown to have a greater negative impact on the stability of the peri-implant mucosa when they are not present are the quality of the mucosa (the presence of attached mucosa), the attachment levels of the adjacent teeth, and the thickness of the mucosa. 28,48 From an esthetic point of view, the gray color of the titanium implant and the implant components may create a major problem when they are exposed and visible as a result of peri-implant mucosal recession. [49][50][51] Unlike natural teeth, recession around implants with a minimal amount of titanium exposure can dramatically impact esthetic appearance, 52 thus being unacceptable to the patient and requiring additional surgical and/or restorative treatment.
In addition, recession defects have also been associated with a deficient band of attached mucosa around the implant, 12 and subsequently, a greater difficulty for patients to properly perform oral hygiene. When implant surfaces become exposed, especially for implants with a rougher surface, 53 plaque accumulation will occur, thus potentially initiating the development of peri-implant disease.

| MANAG EMENT AND PRE VENTI ON OF SOF T TISSUE COMPLIC ATIONS
The management and prevention of soft tissue complications are vital to prevent adverse outcomes in implant dentistry. delivered (E), the treatment of these complications is more complicated and the predictability is reduced. 54 Throughout this review, graded recommendations (highly recommended, recommended, or less recommended) will be given within text boxes for the time point of the treatment, depending on the indication and based on existing and, to some extent, limited evidence.

| Attached and keratinized mucosa
Where there is a lack of attached mucosa, the preferred method of treatment is an apically positioned flap/vestibuloplasty procedure with or without the combination of a graft material. 19 The use of autogenous transplants (free gingival graft or subepithelial connective tissue graft) is considered to be the gold standard, with a reported increase in attached mucosa ranging from 1.4 to 3.3 mm. Other therapeutic treatment modalities include the apically positioned flap/ vestibuloplasty in conjunction with allogenic dermal matrix grafts or a collagen matrix. These options reduce treatment time and patient morbidity but are less well investigated. 19 The therapeutic approach to increase the width of attached mucosa can be more predictably

| Soft tissue volume
Soft tissue grafting procedures to increase mucosal thickness are successfully employed to eliminate soft tissue volume deficiencies around dental implants. For immediate implants, strong evidence suggests that implant placement and simultaneous hard tissue grafting should be combined with a soft tissue graft to counteract contour and remodeling processes following the surgical intervention. The addition of a subepithelial connective tissue graft demonstrated improved esthetics, as assessed by the pink esthetic score and less midfacial recession of the peri-implant soft tissues. [55][56][57] Dental implants may be placed early, delayed, or late. At these time points, remodeling processes may have already led to volume deficiencies. As such, following implant placement with or without For delayed implants, a case series calculated that guided bone regeneration was responsible for 57%, and soft tissue grafting for 43%, of the total final volume. 58 This indicates the importance of soft tissue grafting to enhance the final esthetic outcome. Autogenous tissue (subepithelial connective tissue graft) is considered the treatment of choice for soft volume augmentation around dental implants, resulting in an increase in soft tissue thickness in partially edentulous sites. Free gingival grafts have also been employed but with limited results and decreased color matching. 19 More recently, soft tissue substitutes have been applied, serving as an alternative to a subepithelial connective tissue graft. Based on a randomized controlled clinical trial, employing either a subepithelial connective tissue graft or a newly developed collagen matrix, both treatment options resulted in an increase in soft tissue volume of up to 1.8 mm. However, the use of a newly developed collagen matrix reduced patient morbidity. 18 Later time points for volume or attached mucosa augmentation, especially after the insertion of the definitive reconstruction, are usually not included as part of the regular treatment, and are used instead to compensate for loss of quantity and/or quality of tissue occurring over time. 59 These rescue treatments usually offer a decreased predictability and require more technique-sensitive surgical skills. 54

| Buccal soft tissue recession
The midfacial mucosal level around a dental implant may be influ- Only a few prospective studies have evaluated mucogingival surgical procedures to correct mucosal recessions. 16,54,59 The results, based on the use of coronally advanced flaps in combination with a subepithelial connective tissue graft in all three studies, showed coverage of the recession ranging from 66% to 96%. The implants studied were treated when they were single healthy implants. In a systematic review, 60 it was concluded that mucosal recessions can be treated with an expected gain of 1.6 mm in vertical soft tissue height, but without any long-term evidence of the stability of the tissues. However, midfacial peri-implant soft tissue recession coverage is less successful than recession coverage around natural teeth,

| CLINI C AL CON CEP TS FOR MANAG EMENT AND PRE VENTI ON OF SOF T TISSUE COMPLIC ATIONS AROUND IMPL ANTS
The clinical concepts as presented in the current review is based on a risk assessment of the peri-implant tissues encompassing different

| Clinical concept for prevention of soft tissue complications with implant placement
There are situations when the soft tissue condition is inadequate in volume following tooth extraction but without being sufficiently deficient to contraindicate implant placement. In this situation, the soft tissue augmentation surgery can be performed at the same time as

| Clinical concept for prevention of soft tissue complications within the implant-healing phase
During the implant-healing period, the soft tissue condition can be easily assessed for any lack of volume or lack of attached tissue. Performing the soft tissue augmentation on its own allows for an undisturbed healing phase following implant placement, with or without bone augmentation. Therefore, the use of partial thickness flaps allows for stabilization of the soft tissue grafts without affecting the implant or the bone healing.

| Clinical concept for management of soft tissue complications following delivery of the reconstruction
Once the implant reconstruction is delivered, any soft tissue deficiencies (considered a complication) will be less predictable to treat.
The management of such complications is still possible in some cases. Usually, the most noticeable type of soft tissue complication and cause an esthetic complication to the reconstruction. 16,52,54 Unlike teeth, where minimal recession does not always result in an esthetic concern, patients do not accept the persistence of even minimal recession at the implant site following therapy. 59 In addition, the exposure of the implant creates a favorable environment for plaque accumulation and biofilm formation, which may lead to potential development of peri-implantitis.
Recent evidence has shown the importance of a healthy periimplant mucosa, both from a biologic 19 and an esthetic perspective. 16 According to a current systematic review, 28  The least ideal time for soft tissue augmentation is following insertion of the final reconstruction. This time point is not considered as part of the treatment plan and is usually performed to compensate for severe tissue deficiencies. It can be regarded as a "rescue treatment," is associated with decreased predictability, and is highly technique-sensitive. 54,59 Quite often, the restoration needs to be removed to perform the augmentation surgery. This creates

| CON CLUS ION
The quality and quantity of peri-implant soft tissues are crucial factors and significantly influence biologic and esthetic outcomes in implant dentistry. A proper risk assessment and management of the soft tissues at the planned implant site is important prior to any implant-related surgery. In cases of soft tissue deficiencies, these should be addressed as early as possible to increase the predictability of the surgical interventions.

ACK N OWLED G M ENT
Open Access Funding provided by Universitat Zurich.